Carburetor



Dec. 3, 19.40.

D. FIRTH.

CARBURETOR Filed May 17, 1934 3 Sheets-Sheet l D. FIRTH CARBURETOR FiledMay 1 1934 '3 s-Sheet 2 M G H a w iili: p I y. W

D. FIRTH CARBURE'I'OR Dec. 3, 1940.

Filed May 1'7, 1934 3 Sheets-Sheet 3 r Patented Dec. 3, 1940 UNITEDSTATES PATENT OFFICE CARBURETOR Application May 17, 1934, Serial No.726,059

11 Claims.

The invention relates generally to carburetors for internal combustionengines, and more particularly to a downdraft carburetor.

Carburetors generally may be divided into two general classes so far asthe position of the throttle relatively to the fuel discharge nozzle andintake manifold is concerned, i. e., a posterior throttle carburetorwherein the throttle is positioned behind the nozzle (between the nozzleand intake manifold), so that the nozzle is on the low suction side ofthe throttle, and an anterior throttle carburetor wherein the throttleis in front of the nozzle (the nozzle is positioned inter mediate thethrottle and intake manifold), so

' that the nozzle or fuel discharge device is on the high suction sideof ,the throttle. Each of the two types of carburetors has certainadvantages, and each has certain disadvantages. For example, theposterior throttle carburetor is advantageous inasmuch as the meteringof the fuel is accomplished on the low suction side of the throttle,thereby making it fairly easy to callbrate the fuel discharge means forpart throttle mixtures. A disadvantage of the posterior throttlecarburetor, however, is due to the fact that the throttle, beingpositioned between the fuel discharge device and the intake manifold,interferes with the flow of fuel particularly for wideopen or full-powerthrottle position, thus causing poor distribution of the fuel mixture tothe cylinders. For this reason the anterior throttle carburetor is moreadvantageous so far as wideopen or full-power throttle position isconcerned, since the throttle does not interfere with the flow of fuelmixture. However, because of the location of the fuel discharge devicein the high suction zone of an anterior throttle carburetor,

minute changes in the orifices or jets of the fuel discharge devicescauses considerable change in the mixture ratio.

It is an object of the present invention to provide a new and improvedcarburetor embodying certain advantages of both the posterior and theanterior throttle type carburetor, and at the same time eliminatedisadvantageous features of each which were heretofore pointed out.

Another object is to provide a new and improved downdraft carburetorembodying a fuel discharge means movably mounted in the air passage andarranged so that as the throttle is opened the fuel discharge orifice islowered towards or below the normal fuel level, thus varying the fuelhead and, if desired, providing a syphoning action.

Another object is to provide a new and ima quick response to the demandfor additional 10 fuel.

Another object is to provide a downdraft carburetor embodying a movably'mounted throttle having a main fuel discharge port therein terminatingin an orifice adjacent the edge of the throttle, and means forming afuel supply passage including a duct through the throttle shaft, and ahollow member secured to and swingable with the shaft and extending intothe fuel in the float chamber.

Another object is to provide a new and improved downdraft carburetorconsisting of a relatively small number of parts which may bemanufactured economically.

Another object is to provide a carburetor embodying an accelerating pumpdevice positioned in the float chamber and having its fuel intakecontinuously submerged in the fuel.

Further objects will become readily apparent from the following detaileddescription taken in connection with the accompanying drawings, wherein:l

Figure 1 is a vertical central section through a preferred form of theinvention showing the throttle in a partly open position.

Fig. 1 is a detail view of a modified form of fuel metering pin:

Fig. 2 is a fragmentary section, approximately along the line 2--2 ofFig. 1.

Fig. 3 is a plan view, partly in section, along the line 3--3 of Fig. 1.1

Fig. 4 is a section approximately along the line 4-4 of Fig. 3.

Fig. 5 is a section through a modified form of accelerating pumpconstruction.

Fig. 6 is a similar section through a modified form of the inventionwherein the accelerating pump has been omitted.

Fig. '7 is a fragmentary section through a modified form ofthrottleshaft.

Fig. 8 is a fragmentary section through a modified form of fuel feedingdevice.

While the invention is susceptible of embodiment in many differentforms, there is shown in the drawings and shall herein be described indetail, a preferred embodiment, together with various modificationsthereof, with the understanding that the present disclosure is to beconsidered as an exempliflcation of the principles of the invention andis not intended to limit the invention to the embodiment illustrated.The scope of the invention will be pointed out in the appended claims. 1

Referring to the drawings, and more particularly to Figs. 1 to 4, adowndraft carburetor is illustrated comprising a body casting or member12 having a main passage l3 therethrough, a flange |4 at the lower endadapted for connection to an intake manifold, and a fuel reservoir orfloat bowl l5 providing a fuel chamber l6. A tubular Venturi member I!is secured in the lower portion of the passage l3 by means of a screwdevice l8. A disk-like throttle I9 is movably supported in the passagel3 on a throttle shaft 20 which is rotatably mounted in suitablebearings 2|, 2| formed in the body member on the opposite sides of thepassage l3. A choke valve 22 is carried on a shaft 23 extending acrossthe upper or intake end of the body member, and may be operated in anypreferred or well known manner, for starting purposes.

Fuel is adapted to be supplied to the float bowl |5 by means of asuitable conduit (not shown) which may be connected to a bushing 26secured to the wall of the float bowl as illustrated most clearly inFig. 2. The usual valve 21 is operated by means of a float 28 secured toa pivotally mounted lever 29 so as to maintain the fuel in the chamberl6 at approximately the level indicated by the line 30, Preferably thefloat bowl is provided with a detachable cover 3| having an air vent 32.

In the preferred form of the invention, the fuel discharge meanscomprises a fuel duct or port 35 formed in the throttle I9, the port 35communicating at its inner end with an axially extending passage 36 inthe throttle shaft 20. The passage in the throttle shaft extends into aportion of the shaft which projects into the upper end of the fuelchamber l6 as shown in Fig. 1. Various means may be provided forsupplying fuel from the lower portion of the fuel chamber to the port35, although preferably such means assumes the form of a fuel feedingmember 40 secured to the throttle shaft 20 so as to swing therewith, themember 40 having a passage therethrough connecting at one end with thepassage 36 and at the other end with the surface of said member belowthe fuel level in the chamber l6 as hereinafter more fully described, toform an inlet.

In the form illustrated in Figs. 1 to 4, a tubular fuel feeding member40 is secured at one end to the shaft 20 and extends radially therefromdown into the fuel in the bowl l5. The lower end of the member 40 isclosed by means of an apertured plug 4|, a pin or rod 42, slidablymounted in the aperture 43 of the plug 4| carrying a piston 44 which isslidable in the cylinder formed by the member 40. An inlet fuel passageincludes a plurality of ports 45 in the member 40, ports 46 through thepiston 44, a metering port 41 in a bushing 48 at the upper end of thecylinder, an opening 49 in the upper end of the member 40, and a port 50in the shaft 20. The piston 44 cooperates with the cylinder formed bythe member 40 to form an accelerating pump, the piston being movedupwardly during opening movements of the throttle l9 by means of anarcuate cam member 5| mounted in the lower portion of the fuel bowl. Thepiston rod 42 rides on the cam member 5| so that during swingingmovement of the throttle IS in its shaft 20 (in a clockwise direction asshown in Fig. 2) the piston is moved upwardly or toward the axis of theshaft 20. In the idle position of the throttle valve IS the piston iswithdrawn to the lower portion of the member 40. A coiled springpositioned between a shoulder 56 within the member 40 andan aperturedwasher 51 in the piston 44 serve to move the piston downwa'r dly andmaintain therod 42 in contact with the cam 5|.

In order to-prevent return flow of fuel from the accelerating pumpcylinder, a disk-type check valve 58 is positioned in the lower portionof the hollow piston 44 so as to be adapted to close the ports 46 duringupward movement of the piston. This check valve is of sufficiently lightweight so as to be normally raised by incoming fuel and held in theposition shown in Fig. l. Preferably a metering pin 59 is also carriedby the piston 44, the metering pin having a stem 60 secured to thepiston and being provided with a reduced portion 59'. As illustrated inFig. 1, the stem 60 forms a guide for the check valve 58 and a'flange 6|on the stem serves to locate the apertured washer 51. It will be readilyapparent that when the throttle I9 is moved to its wide-open orfull-power position the reduced portion 59 of the metering pin will bepositioned in theport 41 so as to enlarge the area of the port and passincreased quantities of fuel. The metering pin may assume various formsdepending upon the characteristics desired. Thus, for example, insteadof the twodiameter form of pin illustrated in Fig. 1, a tapered formsuch as illustrated in Fig. 1 may be used. In this form the upper end 59is tapered inwardly and downwardly so as to merge with the reducedportion 59 a stem 60 being provided for securing the pin to theaccelerating pump piston.

As illustrated in Figs. 1 to 4, a separate fuel feeding means isprovided for supplying fuel for idling purposes. This means comprises anidle tube 64 extending down into the fuel bowl l5 and below the normalfuel level therein, the upper end of the idle tube being secured to abushing 65 and provided with a metering orifice B6. A passage 68 in thebody member |2 communicates at its upper end (Fig. 4) with an annularchamber 69 surrounding the bushing 65, and at its lower end with ahorizontal passage 10 communicating with the main carburetor passage l3.The bushing 65 has a plurality of radially extending ports 1| throughwhich fuel passes to the passage 68, and preferably has a port 12 in itsupper end through which air may be bled from a horizontally extendingpassage 13, the inner end of which communicates with the passage l3. Inorder to adjust the amount of fuel and air mixture supplied through thepassage 68, a needle valve 15 is adjustably mounted in the lower portionof the body member l2 and is adapted to control a discharge orifice 16for the passage 10.

In the form of fuel feeding means illustrated in Fig. 5, an orifice 50in the throttle valve shaft 20 is preferably a metering orifice, andfuel is normally fed to said orifice through ports 45 and 46, theapertured washer 51, a transverse, diametrically extending port 80 in abushing 48, and a metering orifice 8| in said bushing. A valve 82normally closes an auxiliary supply port 83 in the bushing 48 and isheld in its closed position by means of a coiled spring 84 positionedbetween the valve 82 and an apertured washer 85. The valve 82 isprovided with a downwardly extending stem 86. In this form of theinvention, as the accelerating piston 44 is moved upwardly a pin 81extending therefrom engagesthe valve stem II to unseat the valve in thewide-open or full power position of the throttle valve. When the valve82 is open, the fuel is metered by the orifice 00. This form of theinvention also provides an air bleed so as to feed an emulsion to theport 35. A passage 88 in the member 40 has a reduced portion 88communicating with a port 08" in the shaft 20, the port 80" connectingwith the passage 36. The outer end of the passage 88 is partly closed bya washer having an opening 09, and a ball check valve 89' positionedbetween said washer and a pin 89" functions to prevent fuel from flowingout through the air bleed passage when the accelerating pump operates.Thus during normal operation the check valve 89' is unseated as shown,and air is admitted through the opening 89, passage 88 and port 88".

As illustrated in Fig. 6, the accelerating pump is omitted. A fuelfeeding member 90 is substituted, said member having a passage 9Icommunicating at its upper end with a radially extending port 92 in thethrottle shaft 20, and also having an air bleed passage 93 communieatingwith a radial port 94 in the shaft 20. In this form. of the invention aplug 95 screw threaded into the lower end of the member 90 has an axialbore 96 normally closed by means of a conical valve 91, radiallyextending ports 98 supplying fuel'to the bore 96. The valve 91 iscarried on a stem09 slidably mounted in the plug 95' and an aperturedwasher I00, and is normally urged downwardly by means of a coiled springIOI. In this form of the invention fuel is fed through a port I02 in theplug 95 until the throttle valve has been swung sufficiently to engagethe lower end of the stem 99 and the cam 5i, after which further openingmovements of the throttle valve unseat the valve 91 and supply addedquantities of fuel through the bore 96.

In Fig. '7 there is illustrated a modified form of idling mechanism.Inithis form of the invention a chamber I05 is formed in the righthandend of the throttle shaft 20" and is connected to the main fuel supplypassage 30" by means of an axial port I06. A needle valve I01 isadjustably mounted in the shaft 20" by means of a threaded stem I08 andmay be operated by means of a thumb nut I09. With the throttle insubstantially horizontal closed position for idling, the port 35 is onthe upper, low suction side of the throttle and thus ineffective to feedfuel. However, in that position of the throttle fuel is drawn into thechamber I05 through the port I06 and discharged into the main carburetorpassage I3 through radially extending ports H and III in the shaft 20"and throttle I9", respectively, on the lower, high suction side of thethrottle. Preferably connecting air bleed ports H2 and H3 are providedin the intake side of the throttle shaft and throttle, respectively, theport II2 being suitably calibrated.

For certain installations, a fuel feeding member II5 of the typeillustrated in Fig. 8 may be employed. In this form the member has twobranches H5 and N5", the branch II5' extending somewhat horizontallyfrom the throttle shaft I20 so as to be above the fuel level 30 in theidle position of the throttle, the branch I15" extending in an inclinedposition downwardly into the fuel. The throttle shaft is provided with ahorizontally extending radial port IIB alined with a passage II! in thebranch 5', and also has a port IIO alined with a passage III in thebranch III". A bushing IN is secured to the outer end of the branch IIIand is provided with a calibrated opening I22, and a bushing I23 securedto the outer end of the branch II!" and is provided with a calibratedopening I23. In this form of the invention, fuel is normally fed throughthe calibrated opening I20, passage H9 and port II8 to the throttleshaft passage 39, air being bled into the same passage 30 through thecalibrated opening I22, passage H1 and port H0. As the throttle isopened, the fuel feeding member H5 is rotated in a clockwise direction(Fig. 8); the calibrated opening I22 being immersed in the fuel at apredetermined point so as to form an auxiliary fuel feed which adds tothe primary fuel feed through the calibrated opening 24 and provides thenecessary additional fuel for the more open and full power positions ofthe throttle.

In the various forms illustrated herein the fuel feeding member 40 isprovided with an irregular opening I 30 through which the reduced andflattened end I3I of the throttle shaft extends. A cap nut I32 isthreaded onto the end of the shaft 20 so as to clamp the fuel feedingmember against a shoulder on the shaft formed by the reduced portionl3l. Thus rotary movement of the fuel feeding member with the shaft isinsured. Preferably, as illustrated in Fig. l, a groove I33 is formed inthe shaft intermediate the ends of -the bearing 2I and a vent I34 isrovided in the body member so as to prevent any syphoning of fuelthrough the bearing should leakage occur.

It is believed readily apparent that the invention provides an extremelysimple carburetor having a relatively small number of parts. Byproviding a fuel discharge orifice which moves downwardly in the bodypassage as the throttle is opened, the fuel head on the orifice may bevaried. 'and if desired the orifice may be moved from a position abovethe normal fuel level in the fuel chamber to a position below the normalfuel level. By locating the discharge orifice in the throttle a simpleconstruction is obtained. and as the throttle is opened the fueldischarge orifice moves downwardly with the incoming air so as toprovide a prompt response to the demand for fuel. By securing the fuelfeeding member to the throttle shaft so thatit swings therewith, thereare no movable joints in the entire fuel supply passage wheredetrimental leakage could occur. Furthermore the fuel supply passage iseffectively protected from the heat of the engine, the portion in thethrottle shaft and throttle being cooled by the incoming air, and theportion within the fuel chamber by the fuel.

As illustrated in the drawings, the accelerating pump actuating cam 5Iis shown with an arcuate form positioned eccentrically of the axis ofthe throttle shaft, but it will be readily evident that the form of themember 5| may be selected so as to provide for any desired movementsofaccelerating pump piston and metering pin.

If desired, the venturi I! may be omitted and the carburetor willoperate satisfactorily. This is due to the fact that with the movablymounted nozzle the device has, in effect, an overflow nozzle in thewide-open position of the throttle.

I claim as my invention:

1. A carburetor having, in combination, a body member forming a mainfuel and air passage and a fuel supply chamber adjacent said passage, athrottle, a shaft rotatably mounted in said body member carrying saidthrottle and having one end thereof extending into said fuel chamber,means for supplying fuel to said main passage comprising a passageway insaid shaft, and a tubular member forming an accelerating pump cylindercarried on said shaft in said fuel chamber and extending downwardly intothe fuel, a piston in said cylinder, means in said fuel chambereffective to actuate said piston during swinging-movement of saidcylinder with said shaft, means including a check-valve-controlledpassage for supplying fuel to said cylinder, and means comprising acheck-valve-controlled passage for normally bleeding air to thepassageway in said shaft, and a check valve in said air bleed passage toprevent discharge of fuel therethrough by the accelerating pump.

2. A carburetor having, in combination, a body member forming a mainfuel and air pasage and a fuel supply chamber adjacent said passage, athrottle, a shaft rotatably mounted in said body member carrying saidthrottle and having one end thereof extending into said fuel chamber,means for supplying fuel to said main passage comprising a passageway insaid shaft, and a tubular member forming an accelerating pump cylindercarried on said shaft in said fuel chamber adapted to swing therewithand extending downwardly into the fuel, a piston in said cylinder, meansin said fuel chamber effective to actuate said piston during swingingmovement of said cylinder with said shaft, means 1 including acheckvalve controlled passage for supplying fuel to said cylinder, meansproviding a metering orifice intermediate the cylinder and shaftpassageway for limiting the flow of fuel to said passageway, meansforming a supplemental outlet from said cylinder to said passageway, avalve normally closing said supplemental outlet, and means on saidpiston for a fuel supply chamber adjacent said passage,

a throttle, a shaft rotatably mounted in said body member carrying saidthrottle and having one end thereof extending into said fuel chamber,means for supplying fuel to said main passage comprising .a passagewayin said shaft, and a tubular member forming an accelerating pumpcylinder carried on said shaft in said fuel chamber adapted to swingtherewith and extending downwardly into the fuel, a piston in saidcylinder, means in said fuel chamber effective to actuate said pistonduring swinging movement of said cylinder with said shaft, and meansincluding a check valve controlled passage for supplying fuel to saidcylinder.

4. A carburetor having, in combination, a body member forming a mainfuel and air passage and a fuel supply chamber adjacent said passage, athrottle, a part rotatably mounted in said body member carrying saidthrottle and having one end thereof extending into said fuel chamber,means for supplying fuel to said main passage comprising a passageway insaid part, and a member forming an accelerating pump cylinder carried onsaid part in said fuel chamber adapted to swing therewith and extendingdownwardly into the fuel, a piston in said cylinder, means in said fuelchamber effective to actuate said piston during swinging movement ofsaid cylinder with said part, means including a check valve controlledpassage through said piston for supplying fuel to said cylinder, meansproviding a metering orifice intermediate the cylinder and saidpassageway for limiting the flowof fuel to said passageway, and ametering pin carried on said piston for controlling said orifice. a

5. A carburetor having,- incombination, a body member forming-a mainpassage for fuel and air and a chamber adjacent said passage for liquidfuel, a throttle in said passage, 2, part movably supporting saidthrottle .and having a portion extending into said chamber, and meansfor feeding liquid-fuel to said passage comprising a fuel feeding membersecured to said part within the fuel chamber and extending downwardlyintothe fuel and a second member extending radially from said part andhaving a passage therethrough terminating in an inletat the outer endthereof, said inlet being above the normal fuel level in said chamber toform an-air bleed when the throttle isin its low speed position andbeing swung down into the'fuel as the throttle is moved toward itshighspeed position to form a supplemental fuel feeding member.

6. A carburetor comprising, in combination, a body member having a mainpassage therethrough, a throttle pivotally mounted in said and an airbleed passage communicating with said discharge port and with said mainpassage anterior to said throttle, and a venturi in said main passageintermediate said throttle and said fuel discharge port.

'7. A carburetor comprising, in combination, a body member having a mainpassage therethrough and a fuel chamber, a throttle in said passagehaving a fuel passage therein terminating in a discharge orifice, ashaft for said throttle having one end projecting into said fuelchamber, a tubular member secured to the end of the throttle shaftwithin the fuel chamber to swing with the throttle, a plunger withinsaid tubular membermounted for reciprocable motion, and cam meansengaging said plunger to reciprocate the same upon swinging movement ofsaid throttle.

8. A carburetor comprising, in combination, a body member having a mainpassage therethrough and a fuel chamber, a throttle in said passagehaving a fuel passage therein terminating in a discharge orifice, athrottle shaft having one end projecting into said fuel chamber andhaving a passage therein communicating with the passage in the throttle,a tubular member disposed within the fuel chamber communicating with thefuel chamber and the passage in said throttle shaft, a plunger mountedfor reciprocable movement within said tubular member, and a cam memberengaged by said plunger, one of said members being rigid with the end ofthe throttle shaft to swing with said throttle, and the other of saidmembers being fixed so as to actuate said plunger by relative movementof the members.

9. A carburetor comprisingyin combination, a body member having a mainpassage therethrough and a fuel chamber, a throttle in said passagehaving a fuel passage therein terminating in a discharge orifice, athrottle shaft having one end projecting into said fuel chamber andhaving a passage in that end communicating with the passage in thethrottle, a tubular member rigid with the end of the throttle shaftprojecting into the fuel chamber providing communication between thefuel chamber and the passage in said shaft, a plunger mounted in saidtubular member for reciprocable movement, an arcuate cam fixed in saidfuel chamber and engaged .by said plunger to reciprocate the same uponmovement of said throttle, and means carried by said plunger varying thecharacter of the passage through said tubular member upon openingmovement of the throttle.

10. A carburetor comprising, in combination, a body member having a mainpassage therethrough, a fuel chamber, a throttl in said passage having.a fuel passage therein terminating in a discharge orifice, and meansfor supplying fuel to the passage in, said throttle including anaccelerating pump disposed in said fuel chamber and comprising a pistonand cylinder device mounted to swing with said throttle, and means toactuate said pump to supply fuel at a rate proportional to the rate atwhich said throttle is opened.

11. A carburetor comprising, in combination, a body member having a mainpassage there through'and a fuel chamber, a throttle in said mainpassage having a fuel passage therein terminating in a-dischargeorifice, and means for supplying fuel to the passage in said throttleincluding a piston and cylinder means forming an accelerating pumpdisposed in said fuel chamber and mounted to swing with said throttle,and means for actuating said pump to discharge fuel when the throttle isswung toward open.

position. i

, DAVID FIRTH. l

